1. Field of the Invention
The present invention relates to a method and an apparatus for processing a substrate, such as a semiconductor wafer and a glass substrate for a liquid crystal display (LCD), by using a chemical liquid and a rinse liquid.
2. Description of the Related Art
In order to obtain a reliable semiconductor device, it is very important to prevent particles from adhering on the wafer surface. Particles can adhere on the wafer surface in any process step in the semiconductor device manufacturing process. For example, JP4-287922A recites that particles are produced during a process for removing a silicon oxide film (i.e., natural oxide film) on a semiconductor wafer by using hydrofluoric acid (HF). In such a process, if a liquid film of HF breaks into droplets, particles can be produced by a reaction between the HF droplets and the surrounding atmosphere at the interface therebetween. The particles thus produced are difficult to remove by the subsequent rinse treatment.
JP4-287922A discloses a method for solving the above problem. The method includes a cleaning step of dissolving the silicon oxide film by HF, and a rinse step of removing HF by a rinse liquid, characterized in that the supply of the rinse liquid starts at the end stage of the cleaning step before stopping the supply of HF. According to the method, the generation of particles, due to the existence of HF in a form of droplet during a time period after stopping the supply of HF and before starting the supply of the rinse liquid, can be prevented.
However, the above method includes the following problem. At the end stage of the cleaning step, a large part of the silicon oxide film has been dissolved to expose the underlying silicon layer (the wafer itself). As the silicon layer is hydrophobic, HF must be supplied at a considerably large supply rate in order to maintain the liquid film of HF over the entire surface of the wafer. This results in increase in consumption of expensive HF, and is not preferable for environmental reasons.